Pop singer JULIAN LENNON is already selling the mountaintop estate he bought last December.

The former World War II bunker, built in the Santa Monica Mountains by the U.S. Army Signal Corps as a radar station, is due to close escrow next week.

The son of the late John Lennon bought the acre-size property after it had been turned into a 4,000-square-foot residence, with a swimming pool and a large yard, for $1,050,000 and sold it for $1.5 million, according to industry sources not involved in the deal.

"It wasn't in as good a condition as when he bought it," one of the sources observed. "He ripped out floors to expose the concrete slab and had letters 5 feet tall painted white on the roof." The letters spelled two words--a coarse British expression for "go away"--to ward off photographers and fans in helicopters and planes, he said.

Actor BURT REYNOLDS, who sold his Holmby Hills house in August for just under $5 million, made the first offer on Lennon's hilltop place at $1.9 million but rescinded it after two weeks, the source added. "He would have scraped (razed) the house and built something new there, because the site is wonderful."

It is on a private road and has 360-degree city and Valley views. The buyer was described as "a man whose name would not be generally recognized, who also plans to knock the house down."

In the meantime, Lennon is also expected to close escrow in about a week on a smaller house off Mulholland Drive. Built in 1950, that house has three bedrooms, including a large master, which is the only room on the second-floor addition.

Actress JULIE ANDREWS and husband, director/producer BLAKE EDWARDS, also are selling the Brentwood house they bought last December for $3.25 million, opting to live full time, instead, in their Malibu home.

The four-bedroom, 6,900-square-foot Brentwood house is in escrow for more than $4 million, including furnishings, sources say. It is being purchased by an executive of a large investment firm.

The house was built in 1988 by Columbia Residential Development, but Andrews and her husband added a garden and a cobblestone driveway.

Actress LINDA EVANS has rented her Beverly Hills-area house to Johnny Carson's TV sidekick ED McMAHON, who is getting a divorce.

McMahon is renting the house for a year at the $12,500-a-month asking price, sources say.

The furnished, 4,000-square-foot house with three bedrooms, two maid's rooms and a heart-shaped lawn, was listed as a rental with Stephen Shapiro of Stan Herman & Associates.

Tom Zutaut, a vice president at Geffen Records who discovered the rock groups GUNS N' ROSES and MOTLEY CRUE, has purchased a home in the Malibu hills, overlooking the Carbon Beach home of his boss, David Geffen.

Zutaut paid in the million-dollar range for his new home, which he bought from Peter Cetera, lead singer of CHICAGO, who moved with his wife and daughter to Aspen. Carol Rapf and Terry O'Connor, both of Jim Rapf & Associates, handled the deal.

Novelist SYDNEY SHELDON just sold an acre in Holmby Hills for $5.5 million in cash. He bought it last year, with a house on it, for $3.75 million, sources say.

He leveled the lot, but left a paddle-tennis court. The house he razed was "an old Regency with a terrible floor plan," said a realtor who did not participate in the sale. The lot is on the same street as the Playboy Mansion and producer AARON SPELLING'S still-unfinished chateau.

A Covina estate, used as a summer residence by descendants of the founder of the 138-year-old SINGER SEWING MACHINE CO., is for sale at $1,975,000. (The founder, Isaac Singer, had 24 children by four different wives.)

The Covina home was used by family members from the time it was built in 1964 until about 15 years ago. The Singer Sewing Machine Co. is based in Stamford, Conn., but opened its West Coast manufacturing headquarters in Glendora in 1958.

The current owner of the home, which was remodeled in 1987, purchased it only a few months ago but decided it is too big for him, so he listed it with Dottie Wrede of Beach & Flaaten Realtors, Arcadia.

The 2.25-acre property has a 5,444-square-foot main residence, a guest house, a pool, fountains, a koi pond, a replica of a Hawaiian waterfall, corrals, a bird aviary, a playground with a musical carrousel, a greenhouse, a 550-gallon underground gasoline tank with a pump and a 10-bed bomb shelter.

Gray Hall--the 13-bedroom, Beverly Hills house once rented by actor DOUGLAS FAIRBANKS and later owned by actor GEORGE HAMILTON and financier BERNIE CORNFELD--was sold recently for $4.35 million.

The 14,000-square-foot, mock-Tudor mansion was sold by local investor Steve Powers and Cornfield, who moved to France, Powers said. The buyer is a Frenchman who represents a leader of the western African country of Burkina Faso, which was known until 1984 as Upper Volta.